I will just dispute three of your arguments. First, household growth (which is what drives housing demand) is affected by migration, but not as you say. The number of households in England is currently projected to grow to 27.5 million in 2033, an increase of 5.8 million (27 per cent) over 2008. This means that 232,000 new houses are required per year. Of this new demand, just over three-fifths is driven by natural population growth (i.e. fertility and life-expectancy levels), with net migration accounting for just under two-fifths.
Second, you criticise my 'chalk and cheese' analogy, when discussing MW's graph showing new migration and waiting lists in the years after 2000. I reassert my point: while it is true that new migrants eventually have an impact on social housing need, they cannot be affecting the current growth in waiting lists if they are (mainly) ineligible to go on them.
Third, to defend the original IH report (although it was nothing to do with me), it is MW itself that drew attention to the extent to which Somali people use social housing, as you can see from their release at http://www.migrationwatchuk.org/pressReleases
Part of the problem with MW is the way that their own releases make exaggerated use of the reports they produce.